1. Field of the Invention
The present invention relates to a ultrasonic motor using ultrasonic vibrations of an elastic member as a driving source, and a ultrasonic motor that can be mounted on a small electronic device such as a catheter.
2. Description of the Related Art
The ultrasonic motor using ultrasonic vibrations of an elastic member as a driving source, with various features which an electromagnetic motor does not have, has been increasingly applied to diverse fields such as electronic devices including a driving source of an autofocus mechanism of a camera, and a medical device that is exposed to an electromagnetic environment. Also, since the ultrasonic motor is easily downsized and has a high degree of freedom in shape, new type ultrasonic motors have been actively researched and developed.
Among the new type ultrasonic motors, it is expected that an ultrasonic motor of a type that transmits ultrasonic vibrations through an acoustic waveguide to a coiled stator and drives a moving member that is disposed in the vicinity of the stator (WO 2005/114824) is applied to, for example, a catheter that can be inserted into an extremely thin portion such as a blood vessel within a human body since the ultrasonic motor can be downsized, and an energy can be supplied from a remote location.
However, the ultrasonic motor of the type which transmits the ultrasonic vibrations to the coiled stator through the acoustic waveguide and drives the moving member that is disposed in the vicinity of the stator cannot efficiently drive the moving member because the ultrasonic vibrations that have been transmitted from the acoustic waveguide are attenuated or affected by reflected waves for the following reasons.
1) A wire that is an acoustic waveguide comes in contact with another member to attenuate the vibrations.
2) The vibrations that have been transmitted through the acoustic waveguide are reflected on a boundary between the stator (coiled) and the acoustic waveguide.
3) The vibration that has been transmitted to the stator is reflected by an end portion of the stator, and is mixed with the vibrations that are transmitted to the stator.
Also, the shape of a coil that constitutes the stator is changed during driving, and the output of the ultrasonic motor is not stabilized.
An object of the present invention is to provide an ultrasonic motor that is simple in structure and high in output and reliability.